The present invention relates to the mechanical engineering, and more particularly, to a labyrinth seal.
The labyrinth seal according to the present invention may be most efficiently used for protecting spindle assembly supports of metal cutting machine tools against penetration of dust and moisture both during shaft rotation and after its stoppage.
The present invention may also be used for sealing rotary shafts and bearing assemblies in the automotive industry, instrumentation engineering, aviation industry and in other fields.
Known in the art is a labyrinth seal of a shaft, comprising a non-rotating axially movable sleeve and a sleeve rigidly fixed to the shaft coaxially therewith. The non-rotating sleeve is made split (of two halves) in the diametrical plane (the plane extending through the shaft axis) and has annular projections on the inner surface of the sleeve.
The outer periphery of the non-rotating sleeve is a cylindrical surface aligning the sleeve in a casing of an assembly being sealed, coaxially with the shaft. The annular projections are rounded at the inner diameter and at points where they mate with the sleeve.
The sleeve fixed to the shaft is an integral part and has annular projections similar to the above-described projections and provided on the outer periphery of the sleeve.
The annular projections are arranged in an alternating fashion in parallel to one another and coaxially with the shaft (cf. U.S. Pat. No. 3,357,708, Cl. 227-56, 1967).
The prior art labyrinth seal is not sufficiently tight at relatively high speed of the shaft, as well as at the moments when the shaft is started or stopped owing to the fact that at high rotary speed of the shaft fluid particles penetrating the space between the annular projections acquire higher energy due to a turbulent stirring of air and fluid particles.
Thus fluid particles fill up the space in the seal between the annular projections and may then enter the assembly bearing sealed. When the shaft is stopped fluid particles penetrating the space between the projections remain in the seal and upon starting they may also penetrate the assembly being sealed. In addition, the seal is not sufficiently tight owing to large spaces between the projections, which cannot be diminished in view of manufacturing difficulties.
Known in the art is also a labyrinth seal of a shaft, comprising ring plates separated by means of spacer rings and arranged in an alternating fashion in parallel with one another and coaxially with the shaft.
One set of ring plates are rigidly fixed to the shaft and the other set of the ring plates are fixed to a casing. One of the end plates secured to the shaft is made of a flexible material (such as rubber) and engages a conical bore of the casing (cf. British patent specification No. 918,999, Cl. F 06 J, 1960).
The prior art labyrinth seal is characterized by high heat release (especially at high rotary speed of the shaft) due to mechanical friction between the flexible plate and conical bore of the casing.
In addition, owing to the rigid installation of the plates in the casing and on the shaft, the seal does not permit to the shaft to move in the axial direction.
Known in the art is a labyrinth seal of a shaft, comprising one outer sleeve and one rotary inner sleeve coaxial therewith, the sleeve being of a circumferential ogee profile facing one another and defining an inner space.
The outer sleeve has in the intermediate portion at least one transverse radial slot which also extends through the inner sleeve. The outer sleeve has a cylindrical outer periphery for a rigid fitting in the casing of a sealed assembly coaxially with the shaft.
The inner sleeve is rigidly fixed on the shaft along the inner cylindrical surface (cf. DT Pat. No. 1650083, Cl. F 16 J 15/44, 1967).
The known labyrinth seal is not sufficiently tight at high rotary speed of the shaft and at stationary shaft owing to the fact that radial slots are provided in the inner rotary sleeve to increase the swirling of fluid particles penetrating the seal and to create pulsating pressure in the interior of the seal in cooperation with the slots of the outer sleeve.
Increased swirling of fluid particles and pulsating pressure at high rotary speed of the shaft result in a material increase in the hydraulic drag of a drain slot, its overfilling with fluid and loss of tightness of the seal.
The circumferential ogee profile of the sleeves features rather low tightness upon stoppage of the shaft. Moreover, the radial slots of the sleeves reduce the working length of the labyrinth and increase local clearances in the seal. This results in low tightness of the seal upon stoppage of the shaft.
In view of more intense swirling of fluid, the seal is characterized by comparatively high heat release.
The provision of slots in the rotary sleeve is also undesirable for high-speed seals in view of possible unbalance.
The disadvantage of the prior art labyrinth seal also resides in complicated manufacture which requires special jigs and equipment.
The outer sleeve is made of a soft alloy (such as aluminium) for the manufacturing reasons.
Thus, in operation in an abrasive medium, the outer sleeve is intensely worn, and the wear products from the seal may penetrate the assembly being sealed.
Since the sleeves are rigidly fixed to the shaft and casing, the seal makes it impossible for the shaft to move axially which may cause, e.g. jamming of bearings upon a temperature expansion of the shaft.
Known in the art is a labyrinth seal of a shaft, comprising ring plates separated by spacer rings and arranged in an alternating fashion in parallel to one another and coaxially with the shaft.
One set of the ring plates are rigidly fixed to the shaft together with a rotary sleeve, and the other set of the ring plates are secured to a non-rotating sleeve.
The non-rotating sleeve is installed in a casing of a spindle assembly coaxially with the shaft. Between the outer cylindrical periphery of the sleeve and the inner surface of the casing there is provided an elastic member enabling, owing to its deformation, an axial displacement of the non-rotating sleeve relative to the stationary casing.
When the shaft rotation is being stopped, the non-rotating sleeve, together with the ring plates and rings secured thereto, is displaced in the axial direction until the rotary and stationary ring plates engage one another. The labyrinth space between the plates is thus closed to provide the seal tightness upon stoppage of the shaft.
When the shaft starts rotating, a hydroaerodynamic lift force appears at the end faces of the plate cooperating with the fluid to shift the non-rotating sleeve axially until identical laybrinth spaces are defined between adjacent rotary and stationary plates. (cf. USSR Inventor's Certificate No. 572622, Int. Cl. F 16 J 15/44) Nov. 14, 1975, publ. Sept. 15, 1977, Off. Bull. No. 34, Moscow).
The prior art labyrinth seal is insufficiently tight at high rotary speed of the shaft, as well as at the moments of starting and stopping the shaft owing to the fact that at high rotary speeds, e.g. during a high-speed grinding, the degree of swirling of fluid flow increases, the fluid comprising a cutting fluid containing abrasive particles. The fluid particles overcome the hydraulic drag of the seal and penetrate the assembly bearing sealed. When the rotation is stopped, a portion of the fluid remains in the seal and may penetrate the assembly being sealed during the shaft starting.